1. Field of the Invention
This invention relates to anchors for boats and other floating vessels. More particularly the invention relates to twin fluke anchors in which the shank can be released to swing freely up to 180.degree. out of the plane of the fluke when necessary to free the anchor from underwater obstructions, which otherwise would prevent hoisting the anchor by hand.
2. Description of the Prior Art
Those who use twin fluke anchors, particularly with small to medium-sized pleasure boats, are aware that in use it is not unusual for an underwater obstruction such as a boulder, log, or the like to become lodged between the flukes and the shank. In a typical twin fluke anchor of the prior art, the swing of the shank out of the plane of the flukes is permanently limited to an acute angle such as 35.degree. on either side of the flukes. When such an anchor catches an underwater obstruction between the flukes and shank, it is very difficult, and sometimes impossible, to retrieve the anchor by hand. On large ships equipped with hoists the problem is not so severe because in many such cases the hoist is powerful enough to pull both anchor and obstruction free from the lake or river bottom; however, most small pleasure craft are not so equipped and many anchors have been abandoned because they could not be retrieved by hand.
Prior workers have attempted to solve the problem of fouled anchors in several ways, none of which is entirely satisfactory.
One approach is exemplified by U.S. Pat. No. 2,856,882; in this approach the flukes are pivotally connected to a hollow shank and the normal swing of the shank is limited by a mechanism associated with spring means located within the shank. Depending on the specific design, either release of the normally restrained spring or a pull gainst the spring force, both accomplished by pulling on the anchoring line from the anchored vessel, causes the restraint on the shank's movement the be removed so that the shank can swing as much as 180.degree. out of the plane of the flukes and the anchor can thereby be pulled clear of the obstruction. On retrieval of the anchor the spring mechanism is reset to again limit swing of the shank. The principal difficulties of this approach are that construction of the anchor is inherently complex due to the necessity for a spring, a hollow shank portion to contain the spring, and at least two parts to the shank (including the hollow portion); material selection is difficult because the spring and associated mechanism must resist the corrosion of various marine environments, which usually requires use of expensive alloys; and in most cases the arrangement is such that the flukes can be released unintentionally, as by the pulling force exerted on the anchoring line if a high wave lifts the anchored vessel.
A second approach to the retrieval of fouled anchors is set forth, for example, in U.S. Pat. No. 3,404,652. In this and several similar patents the normal swing of the shank is limited by one or more frangible elements; when the anchor becomes caught on an obstruction, a pull on the anchoring line is intended to break one of the frangible elements and allow the shank to swing free. One problem with such an anchor is that each time it is extricated from an obstruction by breaking a fragible element, the element must be replaced; although the cost of such elements is presumably low, the necessity for replacement and for keeping spares on hand is an inconvenience. Another problem is that if the frangible elements are not strong enough, an unintended pull, as by a high wave, may cause them to break, whereas if they are too strong it may be impossible to break them when desired.
Other prior approaches to the problem, all of which have difficulties similar to the foregoing, i.e. complexity and/or lack of assured control of when release will occur, include use of spring mechanisms acting on the transverse shaft to which the flukes are attached, exemplified by U.S. Pat. No. 3,045,633, and a design in which a rearward impulsive force mechanism built into the anchor ca be triggered to in effect "kick" the anchor rearwardly out of engagement with the obstruction, as in U.S. Pat. No. 3,518,957.
In view of the shortcomings of prior art devices and the rapid increase of pleasure boating in recent years, there has been a growing need for a simple, yet strong and dependable anchor which can be retrieved by hand when fouled by underwater obstructions. I provide such an anchor which in one embodiment has additional advantages with regard to storage on the boat when not in use.